Method of manufacturing a semiconductor device

ABSTRACT

In a laser irradiation apparatus having low running costs as compared with a conventional apparatus and a laser beam irradiation method using the same, a crystalline semiconductor film having a crystal grain of a grain size equivalent to or larger than a conventional one is formed, and a TFT is manufactured by using the crystalline semiconductor film, so that the TFT enabling a high speed operation is realized. In a case where a laser beam of a short output time from a solid laser as a light source is irradiated to a semiconductor film, another laser beam is delayed from one laser beam, and the laser beams are synthesized to be irradiated to the semiconductor film, so that a cooling speed of the semiconductor film is made gentle, and it becomes possible to form the crystalline semiconductor film having the crystal grain of the grain size equivalent to or larger than that in a case where a laser beam having a long output time is irradiated to the semiconductor film. By manufacturing a TFT using such a crystalline semiconductor film, the TFT enabling the high speed operation can be realized.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of manufacturing asemiconductor device, which includes a step of annealing a semiconductorfilm by using a laser beam. Incidentally, the semiconductor device hereindicates any devices capable of functioning by using semiconductorcharacteristics, and also includes an electro-optic device, such as aliquid crystal display device or a light-emitting device, and anelectronic device including the electro-optic device as a part thereof.

2. Description of the Related Art

In recent years, a technique is widely studied in which a laserannealing is performed on a semiconductor film formed on an insulatingsubstrate of glass or the like to crystallize the film or to improve itscrystallinity. Silicon is often used for the semiconductor film.

As compared with a synthetic quartz glass substrate which isconventionally often used, the glass substrate has merits that it isinexpensive and is rich in workability, and a large area substrate canbe easily manufactured. This is the reason why the study is carried out.The reason why the laser is used for crystallization by preference isthat the melting point of the glass substrate is low. The laser can givehigh energy only to the semiconductor film without raising thetemperature of the substrate very much. Besides, as compared withheating means using an electrothermal furnace, its throughput isremarkably high.

Since a crystalline semiconductor is composed of a number of crystalgrains, it is also called a polycrystalline semiconductor film. Since acrystalline semiconductor film formed through the laser annealing has ahigh mobility, a thin film transistor (TFT) is formed by using thiscrystalline semiconductor film, and it is extensively used for, forexample, a monolithic type liquid crystal electro-optic device in whichTFTs for a pixel portion and a driving circuit are formed on one glasssubstrate.

Besides, a method is used by preference in which a laser annealing isperformed by forming a laser beam oscillated from a pulse oscillatorwith a high output such as an excimer laser into a square spot ofseveral cm square or a line with a length of 10 cm or more on anirradiated surface by an optical system and by scanning the laser beam(or by moving the irradiation position of the laser beam relatively tothe surface to be irradiated), since the method has high productivityand is industrially superior.

Especially, when a linear beam is used, differently from the case wherea spotlike laser beam requiring horizontal and vertical scanning isused, since laser irradiation on the whole surface to be irradiated canbe performed by only scanning in the direction normal to thelongitudinal direction of the linear beam, the productivity is high. Thescanning is performed in the direction normal to the longitudinaldirection since it is the most efficient scanning direction. By thishigh productivity, in the laser annealing method at present, to use thelinear beam obtained by forming a pulse oscillation excimer laser beamthrough a suitable optical system has become the main stream ofmanufacturing technique of a liquid crystal display device using TFTs.

Here, crystallization of a semiconductor film after irradiation of alaser beam to the semiconductor film will be described. When the laserbeam is irradiated to the semiconductor film, the semiconductor ismelted. However, as a time elapses, the temperature of the semiconductorfilm is lowered, and crystal nuclei are created. In the semiconductorfilm, a limitless number of uniform (or irregular) crystal nuclei arecreated and grow, so that crystallization is ended. The positions andsizes of crystal grains obtained in this case are random. As comparedwith the inside of the crystal grain, at the interface of the crystalgrain (crystal grain boundary), there are countless recombinationcenters and trapping centers resulting from amorphous structure, crystaldefects and the like. It is known that if a carrier is trapped by thetrapping center, the potential of the crystal grain boundary is raisedand becomes a barrier against the carrier, so that the current transportcharacteristic of the carrier is lowered. Especially although thecrystallinity of a semiconductor film of a channel formation regionexerts a great influence on the electrical characteristics of a TFT, ithas been almost impossible to remove the influence of the crystal grainboundary and to form the channel formation region by a single crystalsemiconductor film.

Besides, it is known that the growth distance of the crystal grain isproportional to the product of a crystallization time and a growthspeed. Here, the crystallization time is a time, as shown in FIG. 28,from (B) the creation of crystal nuclei in a semiconductor film to (C)the end of crystallization of the semiconductor film. When a time from(A) the start of melting the semiconductor film to (C) the end of thecrystallization is called a melting time, if the melting time isprolonged and the cooling speed of the semiconductor film is made slow,the crystallization time becomes long, and a crystal grain of a largegrain size can be formed.

Although there are various kinds of laser beams crystallization using alaser beam from a pulse oscillation type excimer laser as a light source(hereinafter referred to as an excimer laser beam) is generally used.The excimer laser has merits that its output is high, and repetitiveirradiation at a high frequency is possible, and further. the excimerlaser beam has a merit that an absorption coefficient to a silicon filmis high.

In order to form the excimer laser beam, KrF (wavelength of 248 nm) orXeCl (wavelength of 308 nm) is used as an exited gas. However, there isa problem that a gas such as Kr (krypton) or Xe (xenon) is veryexpensive, and when the frequency of a gas exchange becomes high,manufacturing costs are increased.

Besides, the exchange of additional instruments, such as a laser tubefor laser oscillation and a gas purifier for removing unnecessarycompounds produced in an oscillation process, becomes necessary once intwo to three years. Most of these additional instruments are expensive,and there is a problem that the manufacturing costs are increased aswell.

As described above, although the laser irradiation apparatus using theexcimer laser beam has undoubtedly high performance, it takes much timeand labor in maintenance, and the apparatus has also a defect thatrunning costs (here, costs caused from working) are high for a laserirradiation apparatus for production.

Then, in order to realize a laser irradiation apparatus having lowrunning costs as compared with the excimer laser and to realize a laserannealing method using the same, there is a method using a solid laser(a laser using a crystal rod as an oscillation cavity and for outputtinga laser beam).

It is conceivable that the reason is that although the solid laser atpresent has a large output, an output time is very short. An excitationmethod of the solid laser includes LD (Laser Diode) excitation flashlamp excitation, and the like. In order to obtain a large output by theLD excitation, it is necessary to make a large current flow to the LD.Thus, the lifetime of the LD becomes short, and eventually, the costbecomes high as compared with the flash lamp excitation. By such reason,almost all solid lasers by the LD excitation are small outputapparatuses, and it is under development as a high output laser forindustry at present. On the other hand, since a flash lamp can outputextremely intense light, the laser excited by the flash lamp has a highoutput. However, in the oscillation by the flash tamp excitation,electrons excited by the instantaneously applied energy are emitted atone time, and an output time of the laser becomes very short. Like this,although the solid laser at present has a high output, the output timeis very short. Thus, it is difficult to realize formation of a crystalgrain, which has a grain size equivalent to or larger than a grain sizeformed by laser crystallization using the excimer laser, by lasercrystallization using the solid laser. Incidentally, in the presentspecification, the output time is a half value width in one pulse.

Here, crystallization of a semiconductor film was performed by using aYAG laser as one of typical solid lasers. The YAG laser by the flashlamp excitation was used, and after modulation to the second harmonic bya nonlinear optical element, a silicon film was irradiated. The grainsize of a crystal grain formed by the laser annealing using the YAGlaser was very small as compared with the crystal grain formed by usingthe excimer laser. When a TFT is manufactured by using a crystallinesemiconductor film having such a crystal grain, a large number ofcrystal grain boundaries exist in a channel formation region having animportant influence oil the electrical characteristics of the TFT, whichcause the electrical characteristics to be lowered. It is conceivablethat the reason why only the small crystal grain is formed by the laserannealing using the solid laser is that, as already described, althoughthe solid laser at present has a high output, the output time is veryshort.

SUMMARY OF THE INVENTION

Therefore, in a laser irradiation apparatus having low running costs ascompared with a conventional apparatus and in a laser annealing methodusing the same, an object of the present invention is to provide amethod of manufacturing a semiconductor device by using the laserannealing method for forming a crystal grain having a grain sizeequivalent to or larger than a conventional one.

Since the object of the invention is to form a crystal grain having agrain size equivalent to or larger than a grain size formed by a laserannealing using an excimer laser, a temperature change when an excimerlaser beam was irradiated to a semiconductor film was first calculated.The excimer laser beam was irradiated to a silicon film having astructure shown in FIG. 3, and the temperature with respect to the timewas calculated at points A to C of FIG. 3. Here, the output time of thelaser beam was made 27 ns, and the energy density was made 0.1 to 0.5 J.The results are shown in FIGS. 7A to 7G. From FIGS. 7A to 7G, it isunderstood that as the energy density becomes high, the crystallizationtime and the melting time become long, and the cooling speed becomesgentle. Besides, it is understood that the temperature of the point Cfollows the temperature change of the point A.

It is possible to point out that in order to form a crystal grain of alarge grain size, to make the cooling speed of a semiconductor filmgentle is one of effective means. Specifically, there is a method inwhich an output time of a laser beam is made long and a melting time ofa semiconductor film is made long.

Then, the output time of the YAG laser was prolonged, and calculationwas made on the temperature change when the semiconductor film wasirradiated. As shown in FIG. 3, the laser beam of the YAG laser wasirradiated to the silicon film formed on a silicon oxide film and havinga thickness of 50 nm, and the temperature relative to the time wascalculated at the surface of the silicon film (point A), the interfacebetween the silicon film and the silicon oxide film (point B), and thesilicon oxide film 100 nm below the interface (point C). Here, thetemperature at which the silicon film was melted was made 1200 K. Theresults are shown in FIGS. 4A to 6F. In FIGS. 4A to 4D, the output timewas made 6.7 ns, and the energy density was made 0.15 to 0.4 J. In FIGS.4E to 4H, the output time was made 20 ns, and the energy density wasmade 0.2 to 0.5 J. In FIGS. 5A to 5D, the output time was made 27 ns,and in FIGS. 5E to 5H, the output time was made 50 ns and the energydensity was made 0.2 to 0.5 J. In FIGS. 6A to 6C, the output time wasmade 100 ns, and the energy density was made 0.3 to 0.5 J. In FIGS. 6Dto 6F, the output time was made 200 ns, and the energy density was made0.4 to 0.6 J.

By the irradiation of the laser beam, the temperature at each of thepoints A to C is raised, and after a first constant temperature is kept,it is further raised to reach the highest temperature. Then, thetemperature at each of the points A to C is lowered, and a secondconstant temperature is kept, and there is seen a tendency that thetemperature is further lowered. Since the calculation is made under theassumption that the melting temperature of the silicon film is 1200 K,the silicon film is melted at the first constant temperature, andsolidification (crystallization) of the silicon film occurs at thesecond constant temperature. Here, a time from the start time of thesecond constant temperature to the end time thereof corresponds to thecrystallization time. It is shown that the longer the crystallizationtime is, the gentler the cooling speed is. When a time from the starttime of the first constant temperature to the end time of the secondconstant temperature is made a melting time of the silicon film, at thesame energy density, the longer the output time is, the gentler the timeto the highest temperature reached at each of the points A to C is, andthe melting time becomes long. That is, it can be said that the longerthe output time is, the gentler the cooling speed of the semiconductorfilm is.

FIG. 12 shows the temperature of the silicon oxide film at the starttime of the crystallization with respect to the output time of the laserbeam. From FIG. 12, as the output time becomes long, the temperature ofthe silicon oxide film at the start time of the crystallization israised. When the output time of the laser beam is 50 ns or less thetemperature of the silicon oxide film is sharply lowered. That is, it isunderstood that it is also effective to keep the temperature of theunder film high in order to extend the melting time of the semiconductorfilm.

From the above, as the output time becomes long, the crystallizationtime and the melting time become long, and the cooling speed of thesemiconductor film becomes gentle. Thus, since the creation density ofcrystal nuclei becomes low and the crystallization time becomes long, acrystal grain of a large grain size can be formed. That is, it can besaid that to prolong the output time is effective means for increasingthe grain size of the crystal grain.

However, as already described, although the solid laser at present has alarge output, the output time is very short. For example, while theoutput time of the L4308 type XeCl excimer laser (wavelength of 308 nm)made by Lambda Physic Inc. is 27 ns, the output time of the DCR-3D typeNd:YAG laser (wavelength of 532 nm) made by Spectra-Physics Inc. is 5 to7 ns.

Then, the present invention provides a method of manufacturing asemiconductor device including, as a step, a laser annealing method inwhich in a case where a laser beam having a short output time from asolid laser (a laser using a crystal rod as an oscillation cavity tooutput a laser beam) is irradiated to a semiconductor film, anotherlaser beam is delayed from one laser beam and is irradiated to thesemiconductor film, so that a cooling speed of the semiconductor film ismade gentle. and a crystal grain of a grain size equivalent to or largerthan a case where a laser beam having a long output time is irradiatedto the semiconductor film is formed.

At this time, it is desirable that the laser beam is formed into alinear shape by an optical system and is irradiated. Incidentally, toform the laser beam into the linear shape means that the laser beam isformed so that the shape on an irradiation surface becomes linear. Thatis, it means to form the sectional shape of the laser beam into thelinear shape. Besides, the “linear shape” here does not mean a “line” instrict meaning, but a rectangle (or a long ellipse) having a largeaspect ratio. For example it indicates one having an aspect ratio of 10or more (preferably 100 to 10000).

As the solid laser, what is generally known can be used, and a YAG laser(normally indicating Nd:YAG laser), a YVO₄ laser, a YLF laser, a YAlO₃laser, a glass laser, a ruby laser, an alexandrite laser, Ti:sapphirelaser or the like can be used. Especially, the YVO₄ laser or the YAGlaser excellent in coherency and pulse energy is preferable.

However, since the primary wave (first harmonic) of the YAG laser has along wavelength of 1064 nm, it is preferable to use the second harmonic(wavelength of 532 nm), the third harmonic (wavelength of 355 nm) or thefourth harmonic (wavelength of 266 nm). These harmonics can be obtainedby using a nonlinear crystal.

The first harmonic can be modulated to the second harmonic, the thirdharmonic, or the fourth harmonic by a wavelength modulator including anonlinear element. The respective harmonics may be formed in accordancewith a well-known technique. Besides in the present specification, “alaser beam using a solid laser as a light source” includes not only thefirst harmonic but also the second harmonic, the third harmonic and thefourth harmonic, the wavelength of which is demodulated halfway.

Besides, a Q switch method (Q modulation switch system) often used inthe YAG laser may be used. This is a method in which a Q value issharply raised from a state where the Q value of a laser oscillator ismade sufficiently low so that a steep pulse laser having a very highenergy value is outputted. This is a well-known technique.

In the solid laser used in the present invention, since a laser beam canbe basically outputted if a solid crystal, a resonant mirror, and alight source for exciting the solid crystal exist, it does not take muchtime and labor of maintenance as in the excimer laser. That is, sincethe running costs are very low as compared with the excimer laser, itbecomes possible to greatly reduce the manufacturing costs of asemiconductor device. Besides, if the number of acts of maintenance isreduced, the working rate of a production line is also raised, so thatthe whole throughput of a manufacturing process is improved, and thisgreatly contributes to the lowering of the manufacturing costs of thesemiconductor device. Further, since an occupied area of the solid laseris small as compared with the excimer laser, it is advantageous indesign of a manufacturing line.

According to the present invention, in the laser annealing using a laserbeam having a short output time, a plurality of laser beams areirradiated while a time difference is provided between them, so that acooling speed of a semiconductor film is made gentle, and a time allowedfor crystal growth is prolonged in a process of crystallization, andeventually, enlargement of a grain size of a crystal grain is realized.

By obtaining a crystalline semiconductor film having a large crystalgrain size, it becomes possible to greatly improve the performance ofthe semiconductor device. For example, with respect to a TFT as anexample, when the crystal grain size becomes large, the number ofcrystal grain boundaries contained in a channel formation region can bedecreased. That is, it also becomes possible to manufacture such a TFTthat the channel formation region includes one crystal grain boundary,preferably no crystal grain boundary. Besides, since each crystal grainhas crystallinity substantially regarded as single crystal, it is alsopossible to obtain a high mobility (field effect mobility) equivalent toor higher than a transistor using a single crystal semiconductor.

Further, since it is possible to extremely decrease the number of timeswhen a carrier crosses the crystal grain boundaries, it also becomespossible to reduce fluctuation in an on current value (value of draincurrent flowing when a TFT is in an on state), an off current value(value of drain current flowing when a TFT is in an off state), athreshold voltage, an S value, and a field effect mobility.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing an example of a structure of a laserirradiation apparatus.

FIG. 2 is a view showing an example of a structure of a laserirradiation apparatus.

FIG. 3 is a view showing a structure of a semiconductor film used for asimulation, and temperature observation points.

FIGS. 4A to 4D are views showing temperature changes when a laser beamis irradiated to a semiconductor film under conditions that the outputtime of a YAG laser is 6.7 ns, and the energy density thereof is 0.15 to0.4 J.

FIGS. 4E to 4H are view s showing temperature changes when a laser beamis irradiated to a semiconductor film under conditions that the outputtime of the YAG laser is 20 ns, and the energy density thereof is 0.2 to0.5 J.

FIGS. 5A to 5D are views showing temperature changes when a laser beamis irradiated to a semiconductor film under conditions that the outputtime of a YAG laser is 27 ns, and the energy density thereof is 0.2 to0.5 J.

FIGS. 5E to 5H are views showing temperature changes when a laser beamis irradiated to a semiconductor film under conditions that the outputtime of the YAG laser is 50 ns, and the energy density thereof is 0.2 to0.5 J.

FIGS. 6A to 6C are views showing temperature changes when a laser beamis irradiated to a semiconductor film under conditions that the outputtime of a YAG laser is 100 ns, and the energy density thereof is 0.3 to0.5 J.

FIGS. 6D to 6F are views showing temperature changes when a laser beamis irradiated to a semiconductor film under conditions that the outputtime of the YAG laser is 200 ns, and the energy density thereof is 0.4to 0.6 J.

FIGS. 7A to 7G are views showing temperature changes when a laser beamis irradiated to a semiconductor film under conditions that the outputtime of an excimer laser is 27 ns and the energy density thereof is 0.1to 0.5 J.

FIGS. 8A to 8D are views showing pulse shapes of a YAG laser used for asimulation.

FIGS. 9A to 9F are views showing temperature changes when a YAG laserhaving the pulse shape shown in FIG. 8A is irradiated to a silicon filmhaving the structure shown in FIG. 3 under conditions that energydensity is 0.05 to 0.4 J.

FIGS. 10A to 10C are views showing temperature changes when asemiconductor film is irradiated with a laser beam under conditions thata YAG laser beam is divided into two pulses, one of the pulses isdelayed from the other of the pulses by 10 ns, and the energy density ismade 0.2 to 0.4 J.

FIGS. 10D to 10F are views showing temperature changes when asemiconductor film is irradiated with a laser beam under conditions thatthe YAG laser beam is divided into two pulses, one of the pulses isdelay ed from the other of the pulses by 20 ns, and the energy densityis made 0.2 to 0.4 J.

FIGS. 11A to 11C are views showing temperature changes when asemiconductor film is irradiated with a laser beam under conditions thata YAG laser beam is divided into two pulses, one of the pulses isdelayed from the other of the pulses by 30 ns, and the energy density ismade 0.2 to 0.4 J.

FIG. 12 is a view showing a temperature change of an under film at thecrystallization start time of a semiconductor film with respect to anoutput time of a YAG laser.

FIG. 13 is a view showing a silicon film after irradiation of a singlepulse.

FIG. 14 is a view showing a silicon film after irradiation of doublepulses.

FIG. 15 is a view showing maximum grain sizes of crystal grains formedby irradiation of a single pulse and double pulses to a silicon film.

FIG. 16 is a view showing an example of a structure of a laserirradiation apparatus.

FIGS. 17A to 17C are sectional views showing manufacturing steps of apixel TFT and TFTs of a driving circuit.

FIGS. 18A to 18C are sectional views showing manufacturing steps of thepixel TFT and the TFTs of the driving circuit.

FIGS. 19A and 19C are sectional views showing manufacturing steps of thepixel TFT and the TFTs of the driving circuit.

FIG. 20 is a sectional view showing a manufacturing step of the pixelTFT and the TFTs of the driving circuit.

FIG. 21 is a top view showing a structure of a pixel TFT.

FIG. 22 is a sectional view showing a manufacturing step of an activematrix type liquid crystal display device.

FIG. 23 is a sectional structural view of a driving circuit and a pixelportion of a light-emitting device.

FIG. 24A is a top view of a light-emitting device.

FIG. 24B is a sectional structural view of a driving circuit and a pixelportion of the light-emitting device.

FIGS. 25A to 25F are views showing examples of semiconductor devices.

FIGS. 26A to 26D are views showing examples of semiconductor devices.

FIGS. 27A to 27C are views showing examples of semiconductor devices.

FIG. 28 is a view for explaining a melting time and a crystallizationtime.

FIG. 29 is a view showing an example of a structure of a laserirradiation apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(Embodiment Mode 1)

An embodiment mode for carrying out the invention will be described.

FIG. 1 is a view showing an example of a structure of a laserirradiation apparatus of the present invention. This laser irradiationapparatus includes a solid laser oscillator 101, reflecting mirrors 102,103, 108, 109, 111 to 114, a λ/2 plate 105, thin film polarizingelements (TFP: Thin Film Polarizer) 106 and 107, and an optical system110 for forming a laser beam into a linear shape. Reference numeral 104designates an energy monitor system: and 115, a shutter system.

A laser beam from the laser oscillator 101 is totally reflected by thereflecting mirrors 102 and 103, and reaches the λ/2 plate 105. Theintensity distribution ratio of beams separated by the TFP can bearbitrarily changed by arranging the λ/2 plate 105 on an optical path.

If the TFP 106 is arranged so that the incident angle of the laser beambecomes the Brewster angle, since reflected light of the p-component(component of an electric field vector vibrating on an incident plane(plane determined by an incident light beam and an incident normal)) ofthe laser beam becomes 0, the p-component of the laser beam istransmitted through the TFP, and only the s-component (componentvibrating on a plane vertical to the incident plane) of the laser beamis totally reflected. The transmitted p-component of the laser beam isirradiated to a substrate via the reflecting mirrors 108 and 109 and theoptical system 110.

On the other hand, the totally reflected s-component of the laser beampasses the reflecting mirrors 111 to 114, and then, is totally reflectedby the TFP 107 arranged such that the incident angle becomes theBrewster angle, and is irradiated to the substrate via the reflectingmirrors 108 and 109 and the optical system 110. The s-component of thelaser beam passes the reflecting mirrors 111 to 114, so that an opticalpath length is added to only the s-component of the laser beam, andthere arises an optical path difference between the s-component and thep-component of the laser beam having passed through the TFP 106. A valueobtained by dividing the optical path length by light speed becomes atime difference between the p-component and the s-component when theyare irradiated to the substrate. That is, one pulse laser beam isdivided into two pulses, and an optical path difference is provided toone of the pulses, so that the substrate can be irradiated with thepulses while one of the pulses is delayed from the other of the pulses,and the cooling speed of the semiconductor film can be made gentle.Thus, the creation density of crystal nuclei becomes low and thecrystallization time becomes long, so that a crystal grain of a largegrain size can be formed.

In this embodiment mode of the invention, a laser beam is divided by thes-component and the p-component as polarized components of the laserbeam. Since the s-component and the p-component are componentsindependent of each other. interference does not occur when they aresynthesized. Thus, in the case where a laser oscillator having a highinterference property is used, it is one of very effective dividingmethods. Besides, in the case where the s-component and the p-componentof laser beams oscillated from different laser oscillators aresynthesized, a synthesizing method becomes easy. For example, if anotherlaser oscillator is installed instead of the mirror 114 of FIG. 1, therespective laser beams can be synthesized.

Incidentally, in this embodiment mode of the invention, although thedivision number of one laser beam is made two, the division number isnot limited to two as long as it is plural, and the energy density ofeach of the divided pulses may not be equal to each other. In thisembodiment mode, the energy density can be changed by the λ/2 plate 105.For example, in the case where the energy density of the laser beam ofthe first pulse is higher than the energy density of the laser beam ofthe second or subsequent pulse, since the melting time becomes long, thecooling speed can be made slow. In the case where the energy density ofthe laser beam of the second or subsequent pulse is higher than theenergy density of the laser beam of the first pulse, since thesemiconductor film is heated by the laser beam of the first pulse,further enlargement of the grain size can be expected. The optimumvalues of the added optical path length and the division number of thelaser beam are different according to the state of the semiconductorfilm, the kind of the laser oscillator and the like.

(Embodiment Mode 2)

In this embodiment mode for carrying out the invention, an embodimentmode different from Embodiment Mode 1 will be described. In thisembodiment mode, an example of a laser irradiation apparatus using aplurality of laser oscillators will be described.

FIG. 2 is a view showing an example of a structure of a laserirradiation apparatus of the present invention. This laser irradiationapparatus includes laser oscillators 121 a and 121 b, reflecting mirrors122, 124 and 125, a TFP 123, and an optical system 126 for forming alaser beam into a linear shape.

Laser beams are simultaneously oscillated from the laser oscillators 121a and 121 b. Although not shown, it is assumed that a TFP is used sothat a laser beam 1 emitted from the laser oscillator 121 a has only thes-component, and a laser beam 2 emitted form the laser oscillator 121 bhas only the p-component. After being totally reflected by thereflecting mirror 122, the laser beam 1 reaches the TFP 123. On theother hand, the laser beam 2 reaches the TFP 123 without passing thereflecting mirror and the like. Thus, between the laser beam 1 and thelaser beam 2, an optical path difference is produced by a distancebetween the reflecting mirror 122 and the TFP 123, and a time differenceoccurs when the beams reach a substrate, so that the cooling speed of asemiconductor film becomes gentle. Thus, the creation density of crystalnuclei becomes low and the crystallization time becomes long, so that acrystal grain of a large grain size can be formed. Besides, by changingthe distance between the reflecting mirror 122 and the TFP 123, theoptical path difference between the laser beams emitted from the laseroscillators 121 a and 121 b can be arbitrarily changed.

Further, there is also a method in which when the laser beams areoscillated from the laser oscillators 121 a and 121 b, for example,after the laser oscillator 129 b is oscillated, the laser oscillator 121a is oscillated. As compared with the case where the laser oscillators121 a and 121 b are simultaneously oscillated, since it is not necessaryto form the optical path difference of the reflecting mirror 122 and theTFP 123, a compact laser irradiation apparatus is formed.

As in this embodiment mode of the invention, in the case where thes-component and the p-component of the laser beams oscillated from thedifferent laser oscillators are synthesized, the synthesizing methodbecomes ease. Thus, an optical system does not become complicated, andthis is very effective in optical adjustment, miniaturization of anapparatus, and the like.

Incidentally, in this embodiment mode of the invention, although twolaser oscillators are used, the number is not limited to two as long asit is plural, and the energy density of each of a plurality of plusesmay not be equal to each other. Besides, the optimum values of the addedoptical path length, the number of the laser oscillators, and the likeare different by the state of the semiconductor film, the kind of thelaser oscillator, and the like.

(Embodiment Mode 3)

In this embodiment mode for carrying out the invention, an embodimentmode different from Embodiment Mode 1 and Embodiment Mode 2 will bedescribed. In this embodiment mode, an example of a laser irradiationapparatus using a plurality of laser oscillators will be described.

FIG. 29 is a view showing an example of a structure of a laserirradiation apparatus of the present invention. This laser irradiationapparatus includes laser oscillators 221 a and 221 b, and an opticalsystem 226 for forming a laser beam into a linear shape.

Laser beams are oscillated from the laser oscillators 221 a and 221 bwhile a time difference is produced by an apparatus (not shown) forcontrolling oscillation of a laser. Although optical path lengths fromthe laser oscillators 221 a and 221 b to the optical system 226 areequal to each other, since times at which the laser beams are oscillatedare different from each other, a time difference occurs when the beamsreach a substrate, and the cooling speed of a semiconductor film becomesgentle. Thus, the creation density of crystal nuclei becomes low and thecrystallization time becomes long, so that a crystal grain of a largegrain size can be formed. Besides, by changing the time difference inthe oscillation of the laser beams from the laser oscillators 221 a and221 b, the time difference between the respective laser beams reachingthe substrate can be arbitrarily changed.

In this embodiment mode of the invention, since the optical pathdifference is not formed by adding an optical path length from at leastone laser oscillator of the plurality of laser oscillators to thesubstrate, a compact laser irradiation apparatus is obtained.

Incidentally, in this embodiment mode of the invention, although twolaser oscillators are used, the number is not limited to two as long asit is plural, and the energy density of each of the plurality of laserbeams may not be equal to each other.

The present invention having the above constitution will be describedfurther in detail on the basis of embodiments described below.

[Embodiment 1]

Embodiments of the present invention is explained.

FIG. 1 is a diagram showing an example of a structure of a laserirradiation apparatus of the present invention. The laser irradiationapparatus has the solid state laser oscillator 101, the reflectivemirrors 102, 103, 108, 109, and 111 to 115, the λ/2 plate 105, the thinfilm polarizers (TFPs) 106 and 107, and the optical system 110 forprocessing laser light into a linear shape. Further, reference numeral104 denotes the energy monitor system, and reference numeral 115 denotesthe shutter system. A YAG laser is used as the solid state laseroscillator in the embodiment 1, and the output time of the laser lighthaving the YAG laser as an oscillation source is 6.7 ns.

Laser light from the laser oscillator 101 is reflected by the reflectivemirrors 102 to 104, and arrives at the λ/2 plate 105. By arranging theλ/2 plate 105 in the optical path, the strength distribution ratio ofbeams separated by the TFP 106 can be arbitrarily changed. The strengthsof the two laser lights formed by division using the TFP 106 are made tobe the same in the embodiment 1.

Provided that the TFP 106 is arranged so that the angle of incidence ofthe laser light becomes the Brewster angle, the amount of reflectedlight from the laser light having p components, becomes zero (componentsin which the electric field vector oscillates within the plane ofincidence). The p components of the laser light therefore pass throughthe TFP, and only the s components of the laser light (components inwhich the electric field vector oscillates within a plane vertical tothe plane of incidence) are reflected. The p components of thetransmitted laser light are irradiated on a substrate via the reflectivemirrors 108 and 109, and the optical system 110.

On the other hand, the s components of the reflected laser light arereflected by the TFP 107, arranged so that the angle of incidencebecomes the Brewster angle, after passing through the reflective mirrors111 to 114, and are irradiated to the substrate via the reflectivemirrors 108 and 109, and the optical system 110. By passing the scomponents of the laser light through the reflective mirrors 111 to 114,a light pass length of only the s components of the laser light islengthened, and an optical path difference with the p components of thelaser light that have passed through the TFP 106 is obtained. Adifference in time equal to the value of the lengthened optical pathlength divided by the speed of light is thus formed between the scomponents and the p components when the laser light is irradiated tothe substrate. Namely, when one laser pulse is separated into two pulsesand an optical path length becomes lengthened in one pulse, that pulsecan be delayed longer than the other pulse during irradiation of asubstrate, and the cooling speed of a semiconductor film can be madeslower. The density of nuclei generated therefore becomes lower, thecrystallization time becomes longer, and consequently large size crystalgrains can be formed.

Further, a simulation was performed for the laser irradiation apparatushaving the structure of the embodiment 1 in which, after irradiating oneof the pulses divided to a silicon film, the other pulses are givendelays of 10, 20, and 30 ns and irradiated to the silicon film. It isknown thatdelay time=optical path difference/speed of lightand therefore in order to form delays of 10 ns, the optical path lengthbecomes10×10⁻⁹ [s]×3×10⁸ [m/s]=3 [m]

In other words, the s components of the laser light are irradiated onthe surface to be irradiated with a delay of 10 nm after the pcomponents of the laser light provided that the difference between theoptical path length from the TFP 106 to the TFP 107 via the reflectivemirrors 111 to 114 (the optical path length taken by the s components ofthe laser light in the embodiment 1), and the optical path length fromthe TFP 106 to the TFP 107 (the optical path length taken by the pcomponents of the laser light in the embodiment 1) in FIG. 1 is set to 3m.

The pulse shape of the laser light emitted from the laser oscillators isshown in FIG. 8A. The pulse shown by FIG. 8A is divided into two, andpulse shapes having delays of 10, 20, and 30 ns are as shown in FIGS. 8Bto 8D, respectively. Calculations were performed with the secondharmonics of the YAG laser with the pulse shapes to shown by FIGS. 8B to8D irradiated to a silicon film with the structure shown in FIG. 3, andtemperature versus time was found for the points A to C of FIG. 3.Results are shown in FIGS. 10A to 10C, FIGS. 10D to 10F, and in FIGS.11A to 11C. Note that, for comparison, simulation results for timeversus temperature at the points A to C of FIG. 3 are shown in FIG. 9,for the second harmonic of the YAG laser, having the pulse shape shownin FIG. 8A, irradiated to the silicon film having the structure shown inFIG. 3. The energy density was varied from 0.2 to 0.4 J here. Thecrystallization time and the melting time are short, and in particular,in the condition with low energy density, the temperature of the point Cdoes not follow changes in the temperature of point A in FIGS. 9A to 9F.However, it can be seen that there is a tendency for the crystallizationtime and the melting time to become longer along with lengthening delaytime. In other words, the cooling speed becomes slower by delaying, andthen irradiating, one pulse after irradiation of the other pulse. Thedensity of generated crystal nuclei therefore becomes lower, and thecrystallization time becomes longer, and crystal grains having largesize can be formed. If the TFT is formed by using the crystallinesemiconductor film thus formed, the electrical characteristic of theabove-mentioned TFT become excellent.

Note that although the two laser lights are formed so as to have thesame strengths in the embodiment 1, of course they may also bedifferent. After irradiating the p components of the laser light on thesemiconductor film in the embodiment 1, the s components of the laserlight, which have an optical path length made longer by the reflectivemirrors 111 to 114, are then irradiated to the semiconductor film. Ifthe p components of the laser light are stronger than the s components,it is preferable to irradiate the s components of the laser light beforethe semiconductor film melted by the p components of the laser lightbegins to crystallize. Further, if the strength of the p components ofthe laser light are weaker than the s components of the laser light, itis preferable that the semiconductor film melt after the s components ofthe laser light be irradiated.

[Embodiment 2]

In this embodiment, a crystal grain obtained when a laser beam isirradiated to a semiconductor film by using the laser irradiationapparatus of the embodiment 1 will be described.

First, a semiconductor film is formed on a substrate. In thisembodiment, a 1737 glass substrate of Coming Inc. was prepared as thesubstrate, and an amorphous silicon film having a thickness of 54 nm wasformed by using a plasma CVD method. Subsequently, crystallization ofthe semiconductor film is performed by a laser annealing using a laserbeam. When crystallization is performed by the laser annealing, it isdesirable that hydrogen contained in the semiconductor film is releasedin advance, and it is appropriate that the film is exposed to a nitrogenatmosphere at 400 to 500° C. for about one hour so that a hydrogencontent is made 5 atom % or less in advance. By this, laser-proofproperty of the film is remarkably improved. In this embodiment, thesubstrate was exposed to the nitrogen atmosphere of a temperature of500° C. for one hour.

Then, crystallization of the semiconductor film is performed by usingthe laser irradiation apparatus having the structure of FIG. 1. In thisembodiment, a laser beam was divided into two parts having the sameenergy by the λ/2 plate 105 and the thin film polarizing element 106 sothat double pulses were formed, and after one of the divided pulses wasirradiated to the semiconductor film, the other of the pluses wasirradiated after a delay of 10 ns. For comparison, a laser beam was notdivided but was irradiated, as a single pulse, to the semiconductorfilm. Besides, irradiation was also repeatedly performed at the sameirradiation position while the number of shots was changed.

The results of the experiments are shown in FIGS. 13 and 14. FIGS. 13and 14 show examples of results of observation by a SEM with amagnification of fifty thousand after seco-etching is performed to thesemiconductor film subsequent to laser irradiation. FIG. 13 shows asemiconductor film after the irradiation of 20 shots of single pulses,and FIG. 14 shows a semiconductor film after the irradiation of 12 shotsof double pulses. From FIGS. 13 and 14, it is understood that a crystalgrain of a larger grain size can be obtained when the irradiation isperformed alter the laser beam is divided into two parts. FIG. 15 showsresults of measurement of maximum grain sizes of crystal grains formedwhen the number of shots is changed. Also from FIG. 15, it is understoodthat a crystal grain of a larger grain size can be obtained whenirradiation is performed after the laser beam is divided into two parts.

As described above, it is also experimentally confirmed that when alaser beam is divided and is irradiated to a semiconductor film, acrystal grain of a large size is formed. If a TFT is manufactured byusing a crystalline semiconductor film formed in this way, theelectrical characteristics of the TFT become excellent.

[Embodiment 3]

An embodiment differing from the embodiment 1 is explained in theembodiment 3. An example of a laser irradiation apparatus using aplurality of laser oscillators is shown in the embodiment 3.

FIG. 2 is a diagram showing an example of a structure of a laserirradiation apparatus of the present invention. The laser irradiationapparatus has the laser oscillators 121 a and 121 b, the reflectivemirrors 122, 124, and 125, the TFP 123, and he optical system 126 forprocessing laser light into a linear shape. Two YAG lasers are used asthe laser oscillators in the embodiment 3.

Laser light is emitted at the same time from the laser oscillators 121 aand 121 b. Although not shown in the figure, by using a TFP, the firstlaser light 1 emitted from the laser oscillator 121 a is made to haveonly s components, and the second laser light 2 emitted form the laseroscillator 121 b is made to have only p components. The laser light 1 isreflected by the reflective mirror 122, after which it arrives at theTFP 123. The laser light 2, on the other hand, arrives at the TFP 123without going by way of reflective mirrors and the like. An optical pathdifference is thus formed between the laser light 1 and the laser light2 in accordance with the distance between the reflective mirror 122 andthe TFP 123. A difference in time required to reach a substratedevelops, and the cooling speed of a semiconductor film becomes slower.The density of crystal nuclei that develop therefore becomes lower, andthe crystallization time becomes longer, and large size crystal grainscan be formed. Furthermore, the optical path difference between thelaser lights emitted from the laser oscillators 121 a and 121 b can bearbitrarily changed by changing the distance between the reflectivemirror 122 and the TFP 123.

In addition, there is also a method for oscillating the laser oscillator121 a for example, after oscillating the laser oscillator 121 b, whenemitting laser light from the laser oscillators 121 a and 121 b.Compared to having simultaneous laser light emission from the laseroscillators 121 a and 121 b, optical path differences between thereflective mirror 122 and the TFP 123 need not be formed with thismethod, resulting in a compact laser irradiation apparatus.

[Embodiment 4]

An example of a laser irradiation apparatus combining the embodiment 1and the embodiment 2 is shown in the embodiment 4.

FIG. 13 is a diagram showing an example of a structure of a laserirradiation apparatus of the present invention. The laser irradiationapparatus has solid state laser oscillators 131 a and 131 b, reflectivemirrors 132, 138, 139, and 141 to 145, a λ/2 plate 135, thin filmpolarizers (TFPs) 133, 136, 137, and an optical system 140 forprocessing laser light into a linear shape. Further, reference numeral104 denotes the energy monitor system, and reference numeral 145 denotesa shutter system. Two YAG lasers are used as the solid state laseroscillators in the embodiment 4.

Laser light is emitted at the same time from the laser oscillators 131 aand 131 b. Although not shown in the figure, by using a TFP, the firstlaser light 1 emitted from the laser oscillator 131 a is made to haveonly s components, and the second laser light 2 emitted form the laseroscillator 131 b is made to have only p components. The laser light 1 isreflected by the reflective mirror 132, after which it arrives at theTFP 133. The laser light 2, on the other hand, arrives at the TFP 133without going by way of reflective mirrors and the like. An optical pathdifference is thus formed between the laser light 1 and the laser light2 in accordance with the distance between the reflective mirror 132 andthe TFP 133, and a difference in time for reaching the substratedevelops.

Provided that the TFP 136 is arranged so that the angle of incidence ofthe laser light becomes the Brewster angle, the amount of reflectedlight from the laser light having p components, becomes zero (componentsin which the electric field vector oscillates within the plane ofincidence). The p components of the laser light therefore pass throughthe TFP, and only the s components of the laser light (components inwhich the electric field vector oscillates within a plane vertical tothe plane of incidence) are reflected. The p components of thetransmitted laser light are irradiated on a substrate via the reflectivemirrors 138 and 139, and the optical system 140.

On the other hand, the s components of the reflected laser light arereflected by the TFP 137, arranged so that the angle of incidencebecomes the Brewster angle, after passing through the reflective mirrors141 to 144, and are irradiated to the substrate via the reflectivemirrors 138 and 139, and the optical system 140. By passing through thereflective mirrors 141 to 144, only the s components of the laser lighthave an optical path length that becomes lengthened, and an optical pathdifference with the p components of the laser light which pass throughthe TFP 136 is formed.

A difference in time for the laser lights arriving at the substratetherefore develops in the embodiment 3 due to the optical pathdifference caused by the distance between the reflective mirror 132 andthe TFP 133, and by the optical path difference due to the reflectivemirrors 141 to 144, and the cooling speed of the semiconductor film canbe made slower. The density of crystal nuclei that develop consequentlybecomes less, and the crystallization time becomes longer, and thereforecrystal grains having a large grain size can be formed. By forming theTFT by using the crystalline semiconductor film fabricated in this way,the electronic properties of the above-mentioned TFT can be promoted.

[Embodiment 5]

In this embodiment, the manufacturing method of the active matrixsubstrate is explained using FIGS. 17 to 21.

First, in this embodiment, a substrate 300 is used, which is made ofglass such as barium borosilicate glass or aluminum borosilicate,represented by such as Corning #7059 glass and #1737 glass. Note that,as the substrate 300, a quartz substrate, a silicon substrate, ametallic substrate or a stainless substrate on which is formed aninsulating film. A plastic substrate with heat resistance to a processtemperature of this embodiment may also be used.

Then, a base film 301 formed of an insulating film such as a siliconoxide film, a silicon nitride film or a silicon oxynitride film isformed on the substrate 300. In this embodiment, a two-layer structureis used as the base film 301. However, a single-layer film or alamination structure consisting of two or more layers of the insulatingfilm may be used. As a first layer of the base film 301, a siliconoxynitride film 301 a is formed with a thickness of 10 to 200 nm(preferably 50 to 100 nm) with a plasma CVD method using SiH₄, NH₃, andN₂O as reaction gas. In this embodiment, the silicon oxynitride film 301a (composition ratio Si=32%. O=27%, N=24% and H=17%) with a filmthickness of 50 nm is formed. Then, as a second layer of the base film301, a silicon oxynitride film 301 b is formed and laminated into athickness of 50 to 200 nm (preferably 100 to 150 nm) with a plasma CVDmethod using SiH₁ and N₂O as reaction gas. In this embodiment, thesilicon oxynitride film 301 b (composition ratio Si=32%, O=59%, N=7% andH=2%) with a film thickness of 100 nm is formed.

Subsequently, semiconductor layer 302 are formed on the base film. Thesemiconductor layer 302 are formed from a semiconductor film with anamorphous structure which is formed by a known method (such as asputtering method, an LPCVD method, or a plasma CVD method) into thethickness of from 25 to 80 nm (preferably 30 to 60 nm). The material ofthe crystalline semiconductor film is not particularly limited, but itis preferable to be formed of silicon, a silicon germanium (SiGe) alloy,or the like. In this embodiment, 55 nm thick amorphous silicon film isformed by a plasma CVD method.

The semiconductor film is crystallized next. The laser annealing isapplied to crystallization of the semiconductor film. Further, otherthan laser annealing, thermal crystallization or thermal crystallizationusing nickel as a catalyst are applicable for a crystrallization of thesemiconductor film. The crystallization of the semiconductor film issubjected by a method of combination in which laser annealing and one ofthese crystallization methods above. The laser annealing is implementedby applying the present invention. For example, the laser light, bywhich a solid laser (YAG laser. YVO₄ laser or the like) is set as alight source, is divided into a plurality of laser light. The opticalpath length of a laser light or more to the irradiation surface is madelonger than that of the other laser light to the above-mentionedirradiation surface, and the laser light is irradiated to thesemiconductor film. In this embodiment, after the substrate is exposedin the nitrogen atmosphere of 500° C. temperature for 1 hour, thecrystallization of the semiconductor film is conducted by using thelaser irradiation device shown in FIG. 1, whereby the crystallinesemiconductor film having the crystal grains of large grain size isformed. Here, the YAG laser is used for the laser oscillator. The laserlight modulated into the second harmonic by nonlinear optical element isprocessed into the linear beam by an optical system and irradiated tothe semiconductor film. When the linear beam in irradiated to thesemiconductor film, although the overlap ratio can be set from 50 to98%, the ratio may be set suitably by the operator because the optimumconditions are different according to the state of the semiconductorfilm and the delay time of the laser light.

Thus formed the crystalline semiconductor film is patterned into thedesired shape to form the semiconductor layers 402 to 406. In thisembodiment, the crystalline silicon film is processed patterning byusing the photolithography to form the semiconductor layer 402 to 406.

Further, after the formation of the semiconductor layer 402 to 406, aminute amount of impurity element (boron or phosphorus) may be doped tocontrol a threshold value of the TFT.

A gate insulating film 407 is then formed for covering the semiconductorlayers 402 to 406. The gate insulating film 407 is formed of aninsulating film containing silicon by a plasma CVD method or asputtering method into a film thickness of from 40 to 150 nm. In thisembodiment, the gate insulating film 407 is formed of a siliconoxynitride film into a thickness of 110 nm by a plasma CVD method(composition ratio Si=32%, O=59%. N=7% and H=2%). Of course, the gateinsulating film is not limited to the silicon oxynitride film, and another insulating film containing silicon may be used as a single layeror a lamination structure.

Besides, when the silicon oxide film is used, it can be possible to beformed by a plasma CVD method in which TEOS (tetraethyl orthosilicate)and O₂ are mixed and discharged at a high frequency (13.56 MHZ) powerdensity of 0.5 to 0.8 W/cm² with a reaction pressure of 40 Pa and asubstrate temperature of 300 to 400° C. Good characteristics as the gateinsulating film can be obtained in the manufactured silicon oxide filmthus by subsequent thermal annealing at 400 to 500° C.

Then, as shown in FIG. 17B, on the gate insulating film 407, a firstconductive film 408 with a thickness of 20 to 100 nm and a secondconductive film 409 with a thickness of 100 to 400 nm are formed andlaminated. In this embodiment, the first conductive film 408 of TaN filmwith a film thickness of 30 nm and the second conductive film 409 of a Wfilm with a film thickness of 370 nm are formed into lamination. The TaNfilm is formed by sputtering with a Ta target under a nitrogencontaining atmosphere. Besides the W film is formed by the sputteringmethod with a W target. The W film may be formed by a thermal CVD methodusing tungsten hexafluoride (WF₆). Whichever method is used, it isnecessary to make the material have low resistance for use as the gateelectrode, and it is preferred that the resistivity of the W film is setto less than or equal to 20 μΩcm. By making the crystal grains large, itis possible to make the W film have lower resistivity. However, in thecase where many impurity elements such as oxygen are contained withinthe W film, crystallization is inhibited and the resistance becomeshigher. Therefore, in this embodiment, by forming the W film by asputtering method using a W target with a high purity of 99.9999% and inaddition, by taking sufficient consideration to prevent impuritieswithin the gas phase from mixing therein during the film formation aresistivity of from 9 to 20 μΩcm can be realized.

Note that, in this embodiment, the first conductive film 408 is made ofTaN, and the second conductive film 409 is made of W, but the materialis not particularly limited thereto, and either film may be formed of anelement selected from the group consisting of Ta, W, Ti, Mo, Al, Cu, Cr,and Nd, or an alloy material or a compound material containing the aboveelement as its main constituent. Besides, a semiconductor film, typifiedby a polycrystalline silicon film doped with an impurity element such asphosphorus, may be used. Further, an AgPdCu alloy may be used. Besides,any combination may be employed such as a combination in which the firstconductive film is formed of tantalum (Ta) and the second conductivefilm is formed of W, a combination in which the first conductive film isformed of titanium nitride (TiN) and the second conductive film isformed of W, a combination in which the first conductive film is formedof tantalum nitride (TaN) and the second conductive film is formed ofAl, or a combination in which the first conductive film is formed oftantalum nitride (TaN) and the second conductive film is formed of Cu.

Next, masks 410 to 415 made of resist are formed using aphotolithography method, and a first etching process is performed inorder to form electrodes and wirings. This first etching process isperformed with the first and second etching conditions. In thisembodiment, as the first etching conditions, an ICP (inductively coupledplasma) etching method is used, a gas mixture of CF₄, Cl₂ and O₂ is usedas an etching gas, the gas flow rate is set to 25/25/10 sccm, and plasmais generated by applying a 500 W RF (13.56 MHZ) power to a coil shapeelectrode under 1 Pa. A dry etching device with ICP (Model E645-□ICP)produced by Matsushita Electric Industrial Co. Ltd. is used here. A 150W RF (13.56 MHZ) power is also applied to the substrate side (test piecestage) to effectively apply a negative self-bias voltage. The W film isetched with the first etching conditions, and the end portion of thefirst conductive layer is formed into a tapered shape.

Thereafter, the first etching conditions are chanced into the secondetching conditions without removing the masks 410 to 415 made of resist,a mixed gas of CF₄ and Cl₂ is used as an etching gas, the gas flow rateis set to 30/30 sccm, and plasma is generated by applying a 500 W RF(13.56 MHZ) power to a coil shape electrode under 1 Pa to therebyperform etching for about 30 seconds. A 20 W RF (13.56 MHZ) power isalso applied to the substrate side (test piece stage) to effectively anegative self-bias voltage. The W film and the TaN film are both etchedon the same order with the second etching conditions in which CF₄ andCl₂ are mixed. Note that, the etching time may be increased byapproximately 10 to 20% in order to perform etching without any residueon the gate insulating film.

In the first etching process, the end portions of the first and secondconductive layers are formed to have a tapered shape due to the effectof the bias voltage applied to the substrate side by adopting masks ofresist with a suitable shape. The angle of the tapered portions may beset to 15° to 45°. Thus, first shape conductive layers 417 to 422 (firstconductive layers 417 a to 422 a and second conductive layers 417 b to422 b) constituted of the first conductive layers and the secondconductive layers are formed by the first etching process. Referencenumeral 416 denotes a gate insulating film, and regions of the gateinsulating film which are not covered by the first shape conductivelayers 417 to 422 are made thinner by approximately 20 to 50 nm byetching.

Then, a first doping process is performed to add an impurity element forimparting an n-type conductivity to the semiconductor layer withoutremoving the mask made of resist (FIG. 18A). Doping may be carried outby an ion doping method or an ion implantation method. The condition ofthe ion doping method is that a dosage is 1×10¹³ to 5×10¹⁵ atoms/cm²,and an acceleration voltage is 60 to 100 keV. In this embodiment, thedosage is 1.5×10¹⁵ atoms/cm² and the acceleration voltage is 80 keV. Asthe impurity element for imparting the n-type conductivity, an elementwhich belongs to group 15 of the periodic table, typically phosphorus(P) or arsenic (As) is used, and phosphorus is used here. In this case,the conductive layers 417 to 421 become masks to the impurity elementfor imparting the n-type conductivity, and high concentration impurityregions 306 to 310 are formed in a self-aligning manner. The impurityelement for imparting the n-type conductivity is added to the highconcentration impurity regions 306 to 310 in the concentration range of1×10²⁰ to 1×10²¹ atoms/cm³.

Thereafter, a second etching process is performed without removing themasks made of resist. A mixed gas of CF₄, Cl₂ and O₂ may be used asetching gas used and the W film is selectively etched. The secondconductive layers 428 b to 433 b are formed by a second etching process.On the other hand, the first conductive layers 417 a to 422 a are hardlyetched, and the second conductive layers 428 to 433 are formed.

Next, a second doping process is performed as shown in FIG. 18B withoutremoving the masks from resists. The impurity elements which impartsn-type conductivity is doped under the condition that the dose amount islower than that of a first doping process with an acceleration voltage70 to 120 keV. In this embodiment, the dosage is 1.5×10¹⁴ atoms/cm², andthe acceleration voltage is 90 keV. The second doping process is using asecond shaped conductive layers 428 to 433 as masks, and the impurityelements is doped with a semiconductor layer at the below of the secondconductive layers 428 b to 433 b. High concentration impurity regions423 a to 427 a and low concentration impurity region 423 b to 427 b arenewly formed.

Next, after the masks are removed, masks 434 a and 434 b form resistsare newly formed, and the third etching process is performed as shown inFIG. 18C. A mixed gas of SF₆ and Cl₂ is used as an etching gas the gasflow rate is set to 50/110 sccm, and plasma us generated by applying a500 W RF (13.56 MHZ) power to a coil shape electrode under 1 Pa tothereby perform etching for about 30 seconds. A 10 W RF (13.56 MHZ)power is also applied to the substrate side (test piece stage) toeffectively applied to a negative self-bias voltage. Thus the thirdshape conductive layers 435 to 438 etching a TaN film of the p-channeltype TFT and the TFT of the pixel portion (pixel TFT) by above-mentionedthird etching process.

Next, after removing the masks from resists, the insulating layers 439to 444 is formed, removing selectively the gate insulating film 416 andusing the second shape conductive layer 428. 430 and the second shapeconductive layers 435 to 438 as a mask. (FIG. 19A)

Successively, there is carried out a third doping processing by newlyforming masks 445 a to 445 c comprising resists. By the third dopingprocessing, there are formed impurity regions 446, 447 added with animpurity element for providing a conductive type reverse to theabove-described one conductive type at semiconductor layers constitutingactivation layers of p-channel type TFTs. The impurity regions areformed self-adjustingly by adding the impurity element providing p-typeby using the second conductive layers 435 a, 438 a as masks against theimpurity element. In this embodiment, the impurity regions 446, 447 areformed by an ion doping process using diborane (B₂H₆). (FIG. 19B) In thethird doping processing, the semiconductor layers forming n-channel typeTFTs are covered by the masks 445 a to 445 c comprising resists.Although the impurity regions 446, 447 are added with phosphorus atconcentrations different from each other by the first doping processingand the second doping process in any of the regions, by carrying out thedoping processing such that the concentration of the impurity elementfor providing p-type falls in a range of 2×10²⁰ through 2×10²¹atoms/cm³, the impurity regions function as source regions and drainregions of p-channel ape TFTs and accordingly, no problem is posed. Inthis embodiment, portions of the semiconductor layers constitutingactivation layers of p-channel type TFTs are exposed and accordingly,there is achieved an advantage that the impurity element (boron) is easyto add thereto.

The impurity regions are formed at the respective semiconductor layersby the above-described steps.

Next, a first interlayer insulating film 461 is formed by removing themasks 445 a to 445 c comprising resists. The first interlayer insulatingfilm 461 is formed by an insulating film including silicon and having athickness of 100 through 200 nm by using a plasma CVD process or asputtering process. In this embodiment, a silicon oxynitride film havinga film thickness of 150 nm is formed by a plasma CVD process. Naturally,the first interlayer insulating film 461 is not limited to the siliconoxynitride film but other insulating film including silicon may be usedas a single layer or a laminated structure.

Next, as shown by FIG. 19C, there is carried out a step of activatingthe is impurity elements added to the respective semiconductor layers.The activating step is carried out by a thermal annealing process usinga furnace annealing furnace. The thermal annealing process may becarried out in a nitrogen atmosphere having an oxygen concentrationequal to or smaller than 1 ppm, preferably, equal to or smaller than 0.1ppm at 400 through 700° C. representatively, 500 through 550° C. and inthis embodiment, the activation processing is carried out by a heattreatment at 550° C. for 4 hours. Further, other than the thermalannealing process, a laser annealing process or a rapid thermalannealing process (RTA process) is applicable.

Further, in this embodiment, when the thermal crystallization is alsoapplied using nickel or the like as a catalyst in the crystallizingstep, the metal elements crystallized impurity regions 423 a, 425 a, 426a, 446 a and 447 a including a high concentration of phosphorussimultaneously with the activation processing. Therefore above-mentionedmetal elements are gettered by the above mentioned impurity elements anda metal element concentration in the semiconductor layer mainlyconstituting a channel-forming region is reduced. According to TFThaving the channel forming region fabricated in this way, the offcurrent value is reduced, crystalline performance is excellent andtherefore, there is provided high field effect mobility and excellentelectric properties can be achieved.

Further, the heat treatment may be carried out prior to forming thefirst interlayer insulating film. However, when a wiring material usedis weak at heat, it is preferable to carry out the activation processingafter forming the interlayer insulating film (insulating film whosemajor component is silicon, for example, silicon nitride film) forprotecting wirings as in this embodiment.

Further, there is carried out a step of hydrogenating the semiconductorlayer by carrying out a heat treatment in an atmosphere including 3 to100% of hydrogen at 300 to 550° C. for 1 through 12 hours. In thisembodiment, there is carried out a heat treatment in a nitrogenatmosphere including about 3% of hydrogen at 410° C. for 1 hour. Thestep is a step of terminating dangling bond of the semiconductor layerby hydrogen included in the interlayer insulating film. As other meansof hydrogenation, there may be carried out plasma hydrogenation (usinghydrogen excited by plasma).

Further, when a laser annealing process is used as an activationprocessing, it is preferable to irradiate laser beam of YAG laser or thelike after carrying out the hydrogenation.

Next, there is formed a second interlayer insulating film 462 comprisingan inorganic insulating material or an organic insulating material abovethe first interlayer insulating film 461. In this embodiment, there isformed a acrylic resin film having film thickness of 1.6 μm and there isused a film having a viscosity of 10 to 1000 cp, preferably, 40 through200 cp and formed with projection and recesses at a surface thereof.

In this embodiment, in order to prevent the mirror reflection,projection and recess portions are formed on the surfaces of the pixelelectrodes by forming the second interlayer insulating film withprojection and recess portions on the surface. Also, in order to attainlight scattering characteristics by forming the projection and recessportions on the surfaces of the pixel electrodes, projection portionsmay be formed in regions below the pixel electrodes. In this case, sincethe same photomask is used in the formation of the TFTs, the projectionportions can be formed without increasing the number of processes. Notethat the projection portion may be suitably provided in the pixelportion region except for the wirings and the TFT portion on thesubstrate. Thus, the projection and recess portions are formed on thesurfaces of the pixel electrodes along the projection and recessportions formed on the surface of the insulating film covering theprojection portion.

Also, a film with the leveled surface may be used as the secondinterlayer insulating film 462. In this case, the following ispreferred. That is, after the formation of the pixel electrodes,projection and recess portions are formed on the surface with a processusing a known method such as a sandblast method or an etching method.Thus, since the mirror reflection is prevented and reflection light isscattered, whiteness is preferably increased.

Then, in a driver circuit 506, wirings 463 to 467 electrically connectedwith the respective impurity regions are formed. Note that those wiringsare formed by patterning a lamination film of a Ti film with a filmthickness of 50 nm and an alloy film (alloy film of Al and Ti) with afilm thickness of 500 nm.

Also, in a pixel portion 507, a pixel electrode 470, a gate wiring 469,and a connection electrode 468 are formed (FIG. 20). By this connectionelectrode 468, an electrical connection between a source wiring(lamination layer of the impurity region 443 b and the first conductivelayer 449) and the pixel TFT is formed. Also, an electrical connectionbetween the gate wiring 469 and the gate electrode of the pixel TFT isformed. With respect to the pixel electrode 470, an electricalconnection with the drain region 442 of the pixel TFT and an electricalconnection with the semiconductor layer 458 which functions as one ofelectrodes for forming a storage capacitor are formed. It is desiredthat a material having a high reflectivity such as a film containing Alor Ag as its main constituent, or a lamination film thereof, is used forthe pixel electrode 470.

Thus, the driver circuit 506 having a CMOS circuit formed by ann-channel TFT 501 and a p-channel TFT 502 and an n-channel type TFT 503,and the pixel portion 507 having a pixel TFT 504 and a retainingcapacitor 505 can be formed on the same substrate. As a result, theactive matrix substrate is completed.

The n-channel type TFT 501 of the driver circuit 506 has a channelforming region 423 c, a low concentration impurity region (GOLD region)423 b overlapping with the first conductive layer 428 a constituting aportion of the gate electrode, and a high concentration impurity region423 a which functions as the source region or the drain region. Thep-channel type TFT 502 forming the CMOS circuit by connecting with then-channel type TFT 501 through an electrode 466 has a channel formingregion 446 d, an impurity region 446 b, 446 c formed outside the gateelectrode, and a high concentration impurity region 446 a whichfunctions as the source region or the drain region. The n-channel typeTFT 503 has a channel forming region 425 c, a low concentration impurityregion 425 b (GOLD region) overlapping with the first conductive layer430 a comprising a part of the gate electrode, and a high concentrationimpurity region 425 a which functions as the source region or the drainregion.

The pixel TFT 504 of the pixel portion includes a channel forming region426 c, a low concentration impurity region 426 b (LDD region) formedoutside the gate electrode, and the high concentration impurity region426 a functioning as a source region or a drain region. Besides,impurity elements imparting p-type conductivity are added to therespective semiconductor layers 447 a, 447 b functioning as one of theelectrodes of the storage capacitor 505. The storage capacitor 505 isformed from the electrode (a lamination of 438 a and 438 b) and thesemiconductor layers 447 a to 447 c using the insulating film 444 as adielectric member.

Further, in the pixel structure of this embodiment, an end portion ofthe pixel electrode is formed by arranging it so as to overlap with thesource wiring so that the gap between the pixel electrodes is shieldedfrom light without using a black matrix.

A top view of the pixel portion of the active matrix substratemanufactured in this embodiment is shown in FIG. 21. Note that, the samereference numerals are used to indicate parts corresponding FIGS. 17 to20. A dash line A-A′ in FIG. 20 corresponds to a sectional view takenalong the line A-A′ in FIG. 21. Also a dash line B-B′ in FIG. 20corresponds to a sectional view taken along the line B-B′ in FIG. 21.

This embodiment can be performed by freely combining with theembodiments 1 to 4.

[Embodiment 6]

In this embodiment, an explanation will be given as follows of steps offabricating a reflection type liquid crystal display device from theactive matrix substrate fabricated in the embodiment 5. FIG. 22 is usedin the explanation.

First, in accordance with the embodiment 5, there is provided the activematrix substrate in the state of FIG. 20 and thereafter, an alignmentfilm 567 is formed above the active matrix substrate of FIG. 20, atleast above the pixel electrode 470 and a rubbing processing is carriedout. Further, in this embodiment, before forming the alignment film 567,by patterning an organic resin film such as an acrylic resin film,spacers in a columnar shape 572 are formed at desired positions in orderto maintain an interval between substrates. Further, in place of thespacers in the columnar shape, spacers in a spherical shape may bescattered over an entire face of the substrate.

Next, an opposed substrate 569 is prepared. Successively there areformed color layers 570 and 571 and a leveling film 573. A lightshielding portion is formed by overlapping the color layer 570 of redcolor and the color layer 572 of blue color. Further, the lightshielding portion may be formed by overlapping portions of a color layerof red color and a color layer of green color.

In this embodiment, there is used the substrate shown in the embodiment4. Therefore, in FIG. 21 showing the top view of the pixel portion ofthe embodiment 4, it is necessary to shield at least a gap between thegate wiring 469 and the pixel electrode 470, a gap between the gatewiring 469 and the connection electrode 468 and a gap between theconnection electrode 468 and the pixel electrode 470. In thisembodiment, the respective color layers are arranged such that the lightshielding portions constituted by laminating the color layers overlappositions to be shielded and the opposed substrate is pasted thereto.

A number of steps can be reduced by shielding the gaps among therespective pixels by the light shielding portions constituted bylaminating the color layers in this way without forming light shieldinglayers such as black masks.

Next, the opposed electrode 576 constituted by a transparent conductivefilm is formed on the leveling film 573 at least at the pixel portion,an alignment film 574 is formed over an entire face of the opposedsubstrate and the rubbing processing is carried out.

Further, the active matrix substrate formed with the pixel portion andthe drive circuit and the opposed substrate are pasted together by sealmember 568. The seal member 568 is mixed with fillers, and the twosubstrates are pasted together at a uniform interval therebetween by thefillers and columnar shape spacers. Thereafter, the interval between thetwo substrates is injected with a liquid crystal material 575 and iscompletely sealed by a seal agent (not illustrated). A well-known liquidcrystal material may be used for the liquid crystal material 575. Inthis way, the reflection type liquid crystal display apparatus shown inFIG. 22 is finished. Further, as is necessary, the active matrixsubstrate or the opposed substrate may be divided into a desired shape.Further, a polarizer (not illustrated) is pasted to only the opposedsubstrate. Further, FPC is pasted thereto by using well-knowntechnology.

Thus formed liquid crystal display device have a TFT formed by using thesemiconductor film on which large size crystal grains are formed, andenough operation characteristics and reliability can be realized. Theliquid crystal display device fabricated in this way can be used asdisplay portions of various electronic apparatus.

This embodiment can be performed by freely combining with theembodiments 1 to 5.

[Embodiment 7]

In this embodiment, a description will be given of an example in whichan EL (Electro Luminescence) display device is manufactured as alight-emitting device by using a manufacturing method of a TFT inmanufacturing an active matrix substrate as described in the embodiment5. The EL display device is a light-emitting device including, as alight source, a layer (EL element) containing an organic compound inwhich luminescence is obtained by application of an electric field. TheEL of the organic compound includes light emission (fluorescence)obtained when a singlet excited state is returned to a ground state, andlight emission (phosphorescence) obtained when a triplet excited stateis returned to the ground state. FIG. 23 is a sectional view of a lightemitting device of this embodiment.

Incidentally, in the present specification, any layers formed between ananode and a cathode in a light-emitting element are defined as organiclight-emitting layers. Specifically, the organic light-emitting layerincludes a light-emitting layer, a hole injection layer, an electroninjection layer, a hole transport layer, an electron transport layer,and the like. Basically, the light-emitting element has a structure inwhich an anode layer, a light-emitting layer, and a cathode layer arestacked in sequence, and in addition to this structure, thelight-emitting layer may have a structure in which an anode layer, ahole injection layer, a light-emitting layer and a cathode layer, or ananode layer, a hole injection layer, a light-emitting layer, an electrontransport layer, and a cathode layer are stacked in sequence.

In FIG. 23, a switching TFT 603 provided on a substrate 700 is formed byusing the n-channel TFT 503 of FIG. 22. Accordingly, the description ofthe n-channel TFT 503 may be referred to for a description of itsstructure.

Incidentally, in this embodiment, although a double gate structure inwhich two channel formation regions are formed is adopted, a single gatestructure in which one channel formation region is formed or a triplegate structure in which three channel formation regions are formed maybe adopted.

A driving circuit provided on the substrate 700 is formed by using theCMOS circuit of FIG. 22. Accordingly, the description of the n-channelTFT 501 and the p-channel TFT 502 may be referred to for a descriptionof its structure. Although this embodiment adopts the single gatestructure, the double gate structure or the triple gate structure may beadopted.

Besides, wiring lines 701 and 703 function as source wiring lines of theCMOS circuit, and a wiring line 702 functions as a drain wiring line. Awiring line 704 functions as a wiring line for electrically connecting asource wiring line 708 and a source region of the switching TFT, and awiring line 705 functions as a wiring line for electrically connecting adrain wiring line 709 and a drain region of the switching TFT.

Incidentally, a current control TFT 604 is formed by using the p-channelTFT 502 of FIG. 22. Accordingly, the description of the p-channel TFT502 may be referred to for a description of its structure. Incidentally,although this embodiment adopts the single gate structure, the doublegate structure or the triple gate structure may be adopted.

A wiring line 706 is a source wiring line (equivalent to a currentsupply line) of the current control TFT, and a wiring line 707 is anelectrode which overlaps with a pixel electrode 710 of the currentcontrol TFT so that it is electrically connected to the pixel electrode710.

Incidentally, reference numeral 710 designates the pixel electrode(anode of an EL element) made of a transparent conductive film. As thetransparent conductive film, a compound of indium oxide and tin oxide, acompound of indium oxide and zinc oxide, zinc oxide, tin oxide or indiumoxide can be used. The transparent conductive film added with galliummay be used. The pixel electrode 710 is formed on a flat interlayerinsulating film 711 before the wiring lines are formed. In thisembodiment, it is very important to flatten stepped portions due to theTFTs by using the leveling film 711 made of resin. Since an EL layerformed later is very thin, there is a case where poor light emissionoccurs due to the existence of the stepped portions. Accordingly, it isdesirable to perform flattening before the pixel electrode is formed sothat the EL layer can be formed on the flattest possible surface.

After the wiring lines 701 to 707 are formed, as shown in FIG. 23, abank 712 is formed. The bank 712 may be formed by patterning aninsulating film having a thickness of 100 to 400 nm and containingsilicon or an organic resin film.

Incidentally, since the bank 712 is the insulating film, it is necessaryto be cautious about electro-static damage of the element at the time offilm growth. In this embodiment, carbon particles or metal particles areadded in the insulating film as the material of the bank 712 to lowerthe resistivity and to suppress the generation of static electricity. Atthis time, it is appropriate that the addition amount of the carbonparticle or the metal particle is adjusted so that the resistivitybecomes 1×10⁶ to 1×10¹² Ωm (preferably 1×10⁸ to 1×10¹⁰ Ωm).

An EL layer 713 is formed on the pixel electrode 710. Incidentally.Although only one pixel is shown in FIG. 23, in this embodiment. ELlayers corresponding to R (red), G (green) and B (blue) are separatelyformed. Besides, in this embodiment, a low molecular organic EL materialis formed by an evaporation method. Specifically, a laminate structureis adopted in which a copper phthalocyanine (CuPc) film having athickness of 20 nm is provided as a hole injection layer, and atris-8-quinolinolato aluminum complex (Alq₃) film having a thickness of70 nm is provided thereon as a light-emitting layer. The color of lightemission can be controlled by adding a fluorescent pigment, such asquinacridone, perylene or DCMl, to Alq₃.

However, the above example is an example of the organic EL materialwhich can be used for the EL layer, and it is not necessary to limit theinvention to this. A light-emitting layer, a charge transport layer anda charge injection layer may be freely combined to form an EL layer(layer for light emission and movement of carriers for that). Forexample, although this embodiment shows the example in which the lowmolecular organic EL material is used for the EL layer, a high molecularorganic EL material may be used. Besides, an inorganic material such assilicon carbide can also be used for the charge transport layer or thecharge injection layer. A well-known material can be used as the organicEL material or the inorganic material.

Next, a cathode 714 made of a conductive film is provided on the ELlayer 713. In the case of this embodiment, an alloy film of aluminum andlithium is used as the conductive film. Of course, a well-known MgAgfilm (alloy film of magnesium and silver) may be used. As the cathodematerial, a conductive film made of elements in group 1 or group 2 ofthe periodic table or a conductive film added with those elements may beused.

An EL element 715 is completed at the point of time when the portions upto this cathode 714 are formed. Incidentally, the EL element 715 hereindicates a diode formed of the pixel electrode (anode) 710, the ELlayer 713 and the cathode 714.

It is effective to provide a passivation film 716 so as to completelycover the EL element 715. The passivation film 716 is made of aninsulating film containing a carbon film, a silicon nitride film, or asilicon nitride oxide film, and a single layer of the insulating film ora laminate layer of a combination of those films is used.

At this time, it is preferable to use a film excellent in coverage asthe passivation film, and it is effective to use a carbon film,especially a DLC (diamond-like carbon) film. Since the DLC film can beformed in the temperature range of from room temperature to 100° C., itcan be easily formed over the EL layer 713 which has low heatresistance. Besides, the DLC film has a high blocking effect againstoxygen, and can suppress oxidation of the EL layer 713. Thus, it ispossible to prevent such a problem that the EL layer 713 is oxidizedduring a period when a sealing step subsequent to this is performed.

Further, a sealing member 717 is provided on the passivation film 716,and a cover member 718 is bonded. An ultraviolet ray curing resin may beused for the sealing member 717, and it is effective to provide amaterial having a moisture absorption effect or a material having ananti-oxidation effect in its inside. Besides, in this embodiment, whatis obtained by forming carbon films (preferably diamond-like carbonfilms) on both surfaces of a glass substrate, a quartz substrate or aplastic substrate (including a plastic film) is used as the cover member718.

In this way, the light-emitting device having the structure as shown inFIG. 23 is completed. Incidentally, it is effective that the steps fromthe completion of the bank 712 to the formation of the passivation film716 are continuously performed by using a multi-chamber system (or aninline system) film forming apparatus and without exposing to the air.Moreover, it is also possible to continuously perform the steps up tothe step of bonding the cover member 718 without exposing to the air.

In this way, n-channel TFTs 601 and 602, the switching TFT (n-channelTFT) 603, and the current control TFT (n-channel TFT) 604 are formed onthe insulator 700 using a plastic substrate as a parent substance. Thenumber of masks required in the manufacturing process up to this issmaller than that of a general active matrix type light-emitting device.

That is, the manufacturing process of the TFT is greatly simplified, andthe improvement of yield and the reduction of manufacturing costs can berealized.

Further, as described with reference to FIG. 23, by providing theimpurity region overlapping with the gate electrode through theinsulating film, the n-channel TFT having high resistance againstdeterioration due to a hot carrier effect can be formed. Thus, a highlyreliable light-emitting device can be realized.

Besides, in this embodiment, although only the structure of the pixelportion and the driving circuit is shown, according to the manufacturingprocess of this embodiment, in addition to those, a signal dividingcircuit, a D/A converter, an operational amplifier, and a logicalcircuit such as a γ-correction circuit can be formed on the sameinsulator, and further, a memory and a microprocessor can also beformed.

Further, the EL light-emitting device of this embodiment after the stepsup to the sealing (or encapsulating) step for protecting the EL elementare performed, will be described with reference to FIGS. 24A and 24B.Incidentally, as the need arises, reference numerals used in FIG. 23 arereferred to.

FIG. 24A is a top view showing a state where the steps up to the sealingof the EL element are performed, and FIG. 24B is a sectional view takenalong line C-C′ of FIG. 24A. Reference numeral 801 of a portionindicated by a dotted line designates a source side driving circuit;806, a pixel portion; and 807, a gate side driving circuit. Besides,reference numeral 901 designates a cover member: 902, a first sealmember: and 903, a second seal member, and a sealing member 907 isprovided in the inside surrounded by the first seal member 902.

Incidentally, reference numeral 904 designates a wiring line fortransmitting a signal inputted to the source side driving circuit 801and the gate side driving circuit 807, which receives a video signal anda clock signal from an FPC (Flexible Printed Circuit) 905 as an externalinput terminal. Incidentally, here, although only the FPC is shown, aprinted wiring board (PWB) may be fixed to the FPC. The light-emittingdevice in the present specification includes not only the body of thelight-emitting device, but also a state where the FPC or the PWB isfixed to that.

Next, a sectional structure will be described with reference to FIG.24B. The pixel portion 806 and the gate side driving circuit 807 areformed over the substrate 700, and the pixel portion 806 is formed of aplurality of pixels each including a current control TFT 604 and a pixelelectrode 710 electrically connected to its drain. The gate side drivingcircuit 807 is formed by using a CMOS circuit (see FIG. 14) in which ann-channel TFT 601 and a p-channel TFT 602 are combined.

The pixel electrode 710 functions as an anode of the EL element. Banks712 are formed at both ends of the pixel electrode 710, and an EL layer713 and a cathode 714 of the EL element are formed on the pixelelectrode 710.

The cathode 714 functions also as a wiring line common to all thepixels, and is electrically connected to the FPC 905 through theconnection wiring line 904. Further, all elements included in the pixelportion 806 and the gate side driving circuit 807 are covered with thecathode 714 and the passivation film 716.

Besides, the cover member 901 is bonded by the first seal member 902.Incidentally, a spacer made of a resin film may be provided to ensure aninterval between the cover member 901 and the EL element. The sealingmember 907 is filled in the inside of the first seal member 902.Incidentally, it is preferable to use an epoxy resin for the first sealmember 902 and the sealing member 907. Besides, it is desirable that thefirst seal member 902 is made of a material which blocks permeation ofmoisture or oxygen to the utmost. Further, a material having a moistureabsorption effect or an anti-oxidation effect may be contained in theinside of the sealing member 907.

The sealing member 907 provided so as to cover the EL element functionsalso as an adhesive for bonding the cover member 901. Besides, in thisembodiment. FRP (Fiberglass-Reinforced Plastics), PVF (Polyvinylfluoride), Mylar, polyester, or acryl can be used for a material of aplastic substrate 901 a constituting the cover member 901.

Besides, after the cover member 901 is bonded by using the sealingmember 907, the second seal member 903 is provided so as to cover theside surface (exposed surface) of the sealing member 907. The samematerial as the first seat member 902 can be used for the second sealmember 903.

By sealing the EL element in the sealing member 907 through thestructure as described above, the EL element can be completely isolatedfrom the outside, and it is possible to prevent a material to acceleratethe deterioration by oxidation of the EL layer, such as moisture oroxygen, from invading from the outside. Accordingly, a highly reliablelight-emitting device can be obtained.

The light-emitting device manufactured in the manner as described aboveincludes the TFT manufactured by using the semiconductor film in whichthe crystal grain of the large grain size is formed, and the operationcharacteristics and reliability of the light-emitting device can becomesufficient. Such light-emitting devices can be used as display portionsof various electronic instruments.

Incidentally, this embodiment can be freely combined with Embodiments 1to 5.

[Embodiment 8]

Various semiconductor devices (active matrix type liquid crystal displaydevice active matrix type light-emitting device or active matrix type ECdisplay device) can be formed by applying the present invention.Specifically, the present invention can be embodied in electronicequipment of any type in which such an electrooptical device isincorporated in a display part.

Such electronic equipment is a video camera, a digital camera a digitalcamera a projector, a head-mounted display (goggle type display), a carnavigation system, a car stereo, a personal computer, or a mobileinformation terminal (such as a mobile computer, a mobile telephone oran electronic book). FIGS. 25A-25F, 26A-26D, and 27A-27C show one of itsexamples.

FIG. 25A shows a personal computer which includes a body 2001, an imageinput part 2002, a display part 2003, a keyboard 2004 and the like. Theinvention can be applied to the display part 2003.

FIG. 25B shows a video camera which includes a body 2101, a display part2102, a sound input part 2103, operating switches 2104, a battery 2105,an image receiving part 2106 and the like. The invention can be appliedto the display part 2102.

FIG. 25C shows a mobile computer which includes a body 2201, a camerapart 2202, an image receiving part 2203, an operating switch 2204, adisplay part 2205 and the like. The invention can be applied to thedisplay part 2205.

FIG. 25D shows a goggle type display which includes a body 2301, adisplay part 2302, arm parts 2303 and the like. The invention can beapplied to the display part 2302.

FIG. 25E shows a player using a recording medium on which a program isrecorded (hereinafter referred to as the recording medium) and theplayer includes a body 2401, a display part 2402, speaker parts 2403, arecording medium 2404. operating switches 2405 and the like. This playeruses a DVD (Digital Versatile Disc), a CD and the like as the recordingmedium, and enables a user to enjoy music, movies, games and theInternet. The invention can be applied to the display part 2402.

FIG. 25F shows a digital camera which includes a body 2501, a displaypart 2502, an eyepiece part 2503, operating switches 2504, an imagereceiving part (not shown) and the like. The invention can be applied tothe display part 2502.

FIG. 26A shows a front type projector which includes a projection device2601, a screen 2602 and the like. The invention can be applied to aliquid crystal display device 2808 which constitutes part of theprojection device 2601 as well as other driver circuits.

FIG. 26B shows a rear type projector which includes a body 2701, aprojection is device 2702, a mirror 2703, a screen 2704 and the like.The invention can be applied to the liquid crystal display device 2808which constitutes part of the projection device 2702 as well as otherdriver circuits.

FIG. 26C shows one example of the structure of each of the projectiondevices 2601 and 2702 which are respectively shown in FIGS. 26A and 26B.Each of the projection devices 2601 and 2702 is made of a light sourceoptical system 2801, mirrors 2802 and 2804-2806, a dichroic mirror 2803,a prism 2807, a liquid crystal display device 2808, a phase differenceplate 2809 and a projection optical system 2810. The projection opticalsystem 2810 is made of an optical system including a projection lens.The embodiment 8 is an example of a three-plate type, but it is notlimited to this example and may also be of a single-plate type. Inaddition, those who embody the invention may appropriately dispose anoptical system such as an optical lens, a film having a polarizationfunction, a film for adjusting phase difference or an IR film in thepath indicated by arrows in FIG. 26C.

FIG. 26D is a view showing one example of the structure of the lightsource optical system 2801 shown in FIG. 26C. In the embodiment 8, thelight source optical system 2801 is made of a reflector 2811, a lightsource 2812, lens arrays 2813 and 2814, a polarizing conversion element2815 and a condenser lens 2816. Incidentally, the light source opticalsystem shown in FIG. 26D is one example, and the invention is notparticularly limited to the shown construction. For example, those whoseembody the invention may appropriately dispose an optical system such asan optical lens, a film having a polarization function, a film foradjusting phase difference or an IR film.

The projector shown in FIGS. 26A to 26D is of the type using atransparent type of electrooptical device, but there is not shown anexample in which the invention is applied to a reflection type ofelectrooptical device and a light-emitting device.

FIG. 27A shows a mobile telephone which includes a body 2901, a soundoutput part 2902, a sound input part 2903, a display part 2904,operating switches 2905, an antenna 2906 and the like. The invention canbe applied to the display part 2904.

FIG. 27B shows a mobile book (electronic book) which includes body 3001,display parts 3002 and 3003, a storage medium 3004, operating switches3005, an antenna 3006 and the like. The invention can be applied to thedisplay parts 3002 and 3003.

FIG. 27C shows a display which includes a body 3101, a support base3102, a display part 3103 and the like. The invention can be applied tothe display part 3103. The invention is particularly advantageous to alarge-screen display, and is advantageous to a display having a diagonalsize of 10 inches or more (particularly, 30 inches or more).

As is apparent from the foregoing description, the range of applicationsof the invention is extremely wide, and the invention can be applied toany category of electronic apparatus. Electronic apparatus according tothe invention can be realized by using a construction made of acombination of arbitrary ones of the embodiments 1 to 7.

According to the present invention, at the laser annealing, a laser beamis formed into a linear shape to improve throughput, and further, asolid laser easy to maintain is used, so that the improvement of thethroughput can be achieved as compared with a conventional laserannealing using an excimer laser. Thus, the manufacturing costs of asemiconductor device, such as a TFT or a liquid crystal display deviceformed of TFTs, can be reduced.

Moreover, by performing a laser annealing through such a scheme thatlaser beams provided with a time difference between them are irradiatedto a semiconductor film, it is possible to obtain a crystallinesemiconductor film having a crystal grain of a grain size equivalent toor larger than a conventional size (in a case where an excimer laserbeam is irradiated). By obtaining the crystalline semiconductor filmhaving the large crystal grain size, the performance of thesemiconductor device can be greatly improved.

1. A method of manufacturing a semiconductor device, comprising thesteps of: changing an optical path length of at least one laser beam ofa plurality of laser beams from a plurality of pulse oscillation typesolid lasers as light sources; synthesizing the plurality of laserbeams; and reflecting the synthesized laser beam by at least one mirrorin order to irradiate a semiconductor film.
 2. A method according toclaim 1, wherein an output time of the laser beam is 1 to 50 ns.
 3. Amethod according to claim 1, wherein the pulse oscillation type solidlaser is one selected from the group consisting of a YAG laser, a YVO₄laser, a YLF laser, a YAlO₃ laser, a glass laser, a ruby laser, analexandrite laser, and a Ti:sapphire laser.
 4. A method according toclaim 1, wherein the semiconductor film is a film containing silicon. 5.A method according to claim 1, wherein said semiconductor device isincorporated in a display part of at least one electric equipmentselected from the group consisting of a video camera, a digital camera,a projector, a head-mounted display, a goggle type display, a carnavigation system, a car stereo, a personal computer, a mobileinformation terminal, a mobile computer, a mobile telephone, and anelectronic book.
 6. A method of manufacturing a semiconductor device,comprising the steps of: oscillating a first laser beam from at leastone pulse oscillation type solid laser of a plurality of pulseoscillation type solid lasers; oscillating a second laser beam fromanother pulse oscillation type solid laser; synthesizing the first laserbeam and the second laser beam; and reflecting the synthesized laserbeam by at least one mirror in order to irradiate a semiconductor film.7. A method according to claim 6, wherein an output time of the firstlaser beam or the second laser beam is 1 to 50 ns.
 8. A method accordingto claim 6, wherein the pulse oscillation type solid laser is oneselected from the group consisting of a YAG laser, a YVO4 laser, a YLFlaser, a YAlO3 laser, a glass laser, a ruby laser, an alexandrite laser,and a Ti:sapphire laser.
 9. A method according to claim 6, wherein thesemiconductor film is a film containing silicon.
 10. A method accordingto claim 6, wherein said semiconductor device is incorporated in adisplay part of at least one electric equipment selected from the groupconsisting of a video camera, a digital camera, a projector, ahead-mounted display, a goggle type display, a car navigation system, acar stereo, a personal computer, a mobile information terminal, a mobilecomputer, a mobile telephone, and an electronic book.
 11. A method ofmanufacturing a semiconductor device, comprising the steps of:oscillating a first laser beam from at least one pulse oscillation typesolid laser of a plurality of pulse oscillation type solid lasers;oscillating a second laser beam from another pulse oscillation typesolid laser; changing an optical path length of at least one of thefirst laser beam and the second laser beam; synthesizing the first laserbeam and the second laser beam; and reflecting the synthesized laserbeam by at least one mirror in order to irradiate a semiconductor film.12. A method according to claim 11, wherein an output time of the firstlaser beam or the second laser beam is 1 to 50 ns.
 13. A methodaccording to claim 11, wherein the pulse oscillation type solid laser isone selected from the group consisting of a YAG laser, a YVO4 laser, aYLF laser, a YAlO3 laser, a glass laser, a ruby laser, an alexandritelaser, and a Ti:sapphire laser.
 14. A method according to claim 11,wherein the semiconductor film is a film containing silicon.
 15. Amethod according to claim 11, wherein said semiconductor device isincorporated in a display part of at least one electric equipmentselected from the group consisting of a video camera, a digital camera,a projector, a head-mounted display, a goggle type display, a carnavigation system, a car stereo, a personal computer, a mobileinformation terminal, a mobile computer, a mobile telephone, and anelectronic book.
 16. A method of manufacturing a semiconductor device,comprising the steps of: changing an optical path length of at least onelaser beam of a plurality of laser beams from a plurality of pulseoscillation type solid lasers as light sources; synthesizing theplurality of laser beams; reflecting the synthesized laser beam by atleast one mirror; and forming the synthesized laser beam into a linearshape in order to irradiate a semiconductor film.
 17. A method accordingto claim 16, wherein an output time of the laser beam is 1 to 50 ns. 18.A method according to claim 16, wherein the pulse oscillation type solidlaser is one selected from the group consisting of a YAG laser, a YVO4laser, a YLF laser, a YAlO3 laser, a glass laser, a ruby laser, analexandrite laser, and a Ti:sapphire laser.
 19. A method according toclaim 16, wherein the semiconductor film is a film containing silicon.20. A method according to claim 16, wherein said semiconductor device isincorporated in a display part of at least one electric equipmentselected from the group consisting of a video camera, a digital camera,a projector, a head-mounted display, a goggle type display, a carnavigation system, a car stereo, a personal computer, a mobileinformation terminal, a mobile computer, a mobile telephone, and anelectronic book.
 21. A method of manufacturing a semiconductor device,comprising the steps of: changing an optical path length of at least onelaser beam of a plurality of laser beams from a plurality of pulseoscillation type solid lasers as light sources; synthesizing theplurality of laser beams; dividing the synthesized laser beam into aplurality of laser beams; changing an optical path length of at leastone laser beam of the plurality of laser beams; and synthesizing theplurality of laser beams to irradiate a semiconductor film.
 22. A methodaccording to claim 21, wherein an output time of the laser beam is 1 to50 ns.
 23. A method according to claim 21, wherein the pulse oscillationtype solid laser is one selected from the group consisting of a YAGlaser, a YVO4 laser, a YLF laser, a YAlO3 laser, a glass laser, a rubylaser, an alexandrite laser, and a Ti:sapphire laser.
 24. A methodaccording to claim 21, wherein the semiconductor film is a filmcontaining silicon.
 25. A method according to claim 21, wherein saidsemiconductor device is incorporated in a display part of at least oneelectric equipment selected from the group consisting of a video camera,a digital camera, a projector, a head-mounted display, a goggle typedisplay, a car navigation system, a car stereo, a personal computer, amobile information terminal, a mobile computer, a mobile telephone, andan electronic book.